Flame retardant aromatic polycarbonate resin composition

ABSTRACT

There is provided an aromatic polycarbonate resin composition which exhibits high flame retardancy without sacrificing melt-molding stability or melt fluidity when molding the resin composition. The flame retardant aromatic polycarbonate resin composition comprises a resin component (a) comprising an aromatic polycarbonate and optionally a styrene polymer, the resin composition having an aromatic polycarbonate content of 20% by weight or more; and 0.1 to 50 parts by weight of an organopolysiloxane (b) comprising a linear organopolysiloxane (b)i and a cyclic organopolysiloxane (b)ii, component (b)ii present in an amount of from 5 to 95% by weight based on the total weight of components (b)i and (b)ii.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a flame retardant aromaticpolycarbonate resin composition. More particularly, the presentinvention is concerned with an aromatic polycarbonate resin compositionimparted with flame retardancy by an organopolysiloxane having aspecific structure.

[0003] 2. Background Art

[0004] Aromatic polycarbonates are known engineering plastics which haveexcellent impact resistance, heat resistance and transparency, and havebeen widely used in various fields, especially in the fields of officeautomation machines, household electric appliances and datacommunication equipment. In these fields, there has been a demand formechanical parts having a thin section as well as a complicatedstructure. To meet these demands, the melt fluidity of aromaticpolycarbonates has been increased to achieve high injection moldabilityby adding a styrene resin to the polycarbonate. A rubber-modifiedstyrene resin is generally used for this purpose to achieve desiredproperties such as impact resistance of the resultant aromaticpolycarbonate resin composition.

[0005] An aromatic polycarbonate has a limiting oxygen index (which is acriterion for the flame retardancy) of from 26 to 27, and is known as aresin having a self-extinguishing property. However, in manyelectric/electronic devices, a higher level of flame retardancy isstrictly required to assure the high safety of products.

[0006] As a technique for imparting a high level of flame retardancy toa resin, it is known to incorporate therein flame retardants, forexample halogen-containing flame retardants, phosphorus-containing flameretardants, and auxiliary flame retardants such as antimony oxide.However, in recent years, due to the growing interest in theenvironment, attempts are being made to change the above-mentioned flameretardants to flame retardants having less environmental impact, forexample organopolysiloxanes. The use of organopolysiloxanes as flameretardants is known in the art.

[0007] In general, an organopolysiloxane is a polymer comprisingrecurring units of at least one type of unit selected from the groupconsisting of the following formulae (1) to (4):

[0008] monofunctional structure (M structure);

[0009] bifunctional structure (D structure);

[0010] trifunctional structure (T structure)

[0011] (in formulae (1) to (3), R is a monovalent hydrocarbon group);and

[0012] tetrafunctional structure (Q structure)

[0013] See the SILICONE HANDBOOK, edited by Kunio Ito and published byThe Nikkan Kogyo Shimbun Ltd., Japan (1990)).

[0014] The effect of conventional organopolysiloxanes to impart flameretardancy to a resin is not totally satisfactory, however, and,therefore organopolysiloxanes have generally been used in combinationwith other flame retardants. For example, unexamined Japanese Laid-OpenPatent Application Nos. 51-45160 and 56-100853, Japanese PublishedApplication (Kohyo) No. 59-500099, and unexamined Japanese Laid-OpenPatent Application Nos. 61-241344, 6-306265 and 6-336547 disclose theuse of an organic alkali or alkaline earth metal salt in combinationwith an organopolysiloxane.

[0015] Further, unexamined Japanese Laid-Open Patent Application Nos.3-143951, 10-139964, 11-140294, 11-217494 and 11-222559 each disclose amethod of improving the flame retardancy of a resin by using anorganopolysiloxane having an appropriately branched structure as a flameretardant.

[0016] An organopolysiloxane having a branched structure, hereinafter,simply referred to as a “branched organopolysiloxane” mainly comprisestrifunctional (i.e., T structure, RSiO_(3/2)) and/or tetrafunctionalstructures (i.e., Q structure, SiO_(4/2)) of the four types of unitsmentioned above. However, the flame retarding effect of the branchedorganopolysiloxane is still unsatisfactory. The branchedorganopolysiloxane, in general, is resinous and has a high silicon atomcontent and, therefore, when such a branched organopolysiloxane isincorporated into a resin such as an aromatic polycarbonate, it lowersthe fluidity of the resin.

[0017] Due to the branched structure, branched organopolysiloxanes havea high content of reactive terminal groups, such as silanol groups i.e.,a hydroxyl group directly bonded to a silicon atom, or an alkoxysilylgroup. For this reason, the organopolysiloxane per se is not onlyunstable at high temperatures, but also is likely to decompose thearomatic polycarbonate when kneaded therewith. The occurrence of thesedisadvantageous phenomena is markedly increased when a low molecularweight organopolysiloxane is used so as to improve kneadability with thearomatic polycarbonate. This is because the terminal group content ofthe organopolysiloxane molecules is increased due to the use of the lowmolecular weight organopolysiloxane molecules.

SUMMARY OF THE INVENTION

[0018] It is a primary object of the present invention to provide anaromatic polycarbonate resin composition which exhibits high flameretardancy without sacrificing the melt stability or the melt fluidityin molding the resin composition. The present inventors have madeextensive studies with a view toward attaining the object of the presentinvention by using an organopolysiloxane comprising substantiallybifunctional moieties (i.e., D structure, R₂SiO_(1/2)). As a result, ithas unexpectedly been found that a resin composition may be preparedcomprising an aromatic polycarbonate, and incorporated therein,organopolysiloxanes comprising in combination a linearorganopolysiloxane comprised of recurring D units and a cyclicorganopolysiloxane comprised of recurring D units. In such compositions,not only can the dispersibility of the organopolysiloxanes in the resinbe improved, but also the resin composition exhibits excellent flameretardancy. In particular, the dripping of flaming particles isprevented when the resin composition burns. The present invention hasbeen completed, based on this novel finding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] According to the present invention, there are provided flameretardant aromatic polycarbonate resin compositions comprising 100 partsby weight of a resin component (a) containing an aromatic polycarbonateand optionally a styrene polymer, wherein the resin mixture has anaromatic polycarbonate content of 20% by weight or more, and 0.1 to 50parts by weight of an organopolysiloxane (b) comprising at least onelinear organopolysiloxane (b)i and at least one cyclicorganopolysiloxane (b)ii wherein the organopolysiloxane (b) containscomponent (b)ii in an amount of from 5 to 95% by weight, based on thetotal weight of components (b)i and (b)ii,

[0020] the at least one linear organopolysiloxane (b)i being representedby the following formula (5):

[0021] wherein:

[0022] n represents an integer of 2 or more;

[0023] each R¹ independently represents a monovalent C₆-C₂₀ hydrocarbongroup containing an aromatic group;

[0024] each R² independently represents a monovalent C₁-C₂₀ hydrocarbongroup containing no aromatic group; and

[0025] each of R³ and R⁴ independently represents a hydrogen atom or atriorganosilyl group SiR⁵ ₃, wherein each R⁵ independently represents amonovalent C₁-C₂₀ hydrocarbon group; and

[0026] the at least one cyclic organopolysiloxane (b)ii beingrepresented by the following formula (6):

[0027] wherein m represents an integer of 3 or more; and

[0028] R¹ and R² are as defined for formula (1) above.

[0029] The invention further provides further compositions according tothose just described, wherein each R¹ in formulae (5) and (6) is aphenyl group and each R² in formulae (5) and (6) is a methyl group.

[0030] Resin component (a) used in the present invention comprises anaromatic polycarbonate optionally containing a styrene polymer.

[0031] In the present invention, the aromatic polycarbonate used asresin component (a) is an aromatic polycarbonate having a main chaincomprising recurring units represented by the following formula (7):

[0032] (wherein Ar is the residue of a bifunctional phenolic compound).Such aromatic polycarbonates can be produced, for example, by a reactionbetween a bifunctional phenolic compound and a carbonate precursor; areaction between a bifunctional phenolic compound and a carbonatemonomer; or a polymerization reaction of a carbonate prepolymer.

[0033] For purposes of illustration, examples of methods for producingaromatic polycarbonates include an interfacial polymerization method,i.e., a phosgene method, in which a bifunctional phenolic compound isreacted with phosgene in the presence of an aqueous sodium hydroxidesolution and methylene chloride as a solvent; a transesterificationmethod i.e., a molten-state transesterification in which a bifunctionalphenolic compound and diphenyl carbonate are subjected totransesterification; and a solid-phase polymerization method in which acrystallized carbonate prepolymer is used.

[0034] Examples of bifunctional phenolic compounds include2,2-bis(4-hydroxyphenyl)propane (bisphenol A),2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,1,1-bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)methane,4,4′-dihydroxydiphenyl, 4,4′-dihydroxy-3, 3′, 5,5′-tetramethyldiphenyl,1,1-bis(4-hydroxyphenyl)cyclohexane,1-phenyl-1,1-bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)ether,bis(4-hydroxyphenyl)ketone, bis(4-hydroxyphenyl)sulfide,bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide,hydroquinone, resorcinol and catechol. 2,2-bis(4-hydroxyphenyl)propane(bisphenol A) is particularly preferred. In the present invention, thesebi-functional phenolic compounds can be used individually or incombination.

[0035] It is preferred that the aromatic polycarbonate used in thepresent invention is an aromatic polycarbonate containing substantiallyno halogens in the structure thereof. From the viewpoint of mechanicalstrength and moldability, the viscosity average molecular weight of thearomatic polycarbonate is preferably in the range of from 10,000 to100,000 Da (Daltons), more preferably in the range of from 14,000 to40,000 Da. The viscosity average molecular weight of an aromaticpolycarbonate can be determined from the solution viscosity of thearomatic polycarbonate using methylene chloride as a solvent.

[0036] In the present invention, the styrene polymer optionallycontained in the resin mixture used as resin component (a) may be arubber-modified styrene polymer and/or a non-rubber-modified styrenepolymer. A rubber-modified styrene polymer alone, or a mixture ofrubber-modified styrene polymer and non-rubber-modified styrene polymerare preferred.

[0037] A rubber-modified styrene polymer is a polymer having a structurein which a dispersion phase comprised of a particulate rubber polymerfor modification is dispersed in a continuous phase comprised of astyrene polymer. A rubber-modified styrene polymer can be obtained bygraft-polymerizing an aromatic vinyl monomer such as styrene,a-methylstyrene or p-methylstyrene and optionally other comonomerscopolymerizable with the aromatic vinyl monomer, onto a rubber polymer.Customary methods such as bulk polymerization, emulsion polymerization,or suspension polymerization may be employed.

[0038] Examples of rubber polymers suitable for modification includediene rubbers such as polybutadiene, poly(styrene-butadiene) andpoly(acrylonitrile-butadiene); isoprene rubbers; chloroprene rubbers;acrylic rubbers such as polybutyl acrylate; ethylene/propylene/dieneterpolymers (EPDM); and ethylene/octene copolymer rubbers.

[0039] Examples of comonomers copolymerizable with the aromatic vinylmonomer include unsaturated nitrile monomers such as acrylonitrile andmethacrylonitrile; and vinyl monomers such as acrylic acid, methacrylicacid, maleic anhydride and N-substituted maleimides.

[0040] In the present invention, the content of the rubber polymeremployed in modifying the rubber-modified styrene polymer is preferablyin the range of from 2 to 50% by weight, more preferably from 5 to 30%by weight. When the content of the rubber polymer in the rubber-modifiedstyrene polymer is less than 2% by weight, the impact resistance of therubber-modified styrene polymer is low, while when the content of therubber polymer is more than 50% by weight, the rubber-modified polymersuffers not only a decrease in heat stability and stiffness, but also alowering of melt fluidity and the occurrence of discoloration andgelation. The average diameter of the rubber polymer particles in therubber-modified styrene polymer is preferably from 0.1 to 5.0 μm, morepreferably from 0.2 to 3.0 μm.

[0041] Preferred examples of rubber-modified styrene polymers includeso-called high impact polystyrene (hereinafter, frequently referred toas “HIPS”), acrylonitrile/butadiene/styrene copolymer (ABS resin),acrylonitrile/acrylic rubber/styrene copolymer (AAS resin),acrylonitrile/ethylene-propylene rubber/styrene copolymer (AES resin)and methyl methacrylate/butadiene/styrene copolymer (MBS resin).

[0042] A non-rubber-modified styrene polymer is a polymer obtained bysubstantially the same method as described in connection with therubber-modified styrene polymer except that a rubbery polymer is notused. That is, a non-rubber-modified styrene polymer can be obtained bypolymerizing or copolymerizing an aromatic vinyl monomer such asstyrene, α-methylstyrene, or p-methylstyrene and optionally anunsaturated nitrile monomer (such as acrylonitrile or methacrylonitrile)or other monomers such as acrylic acid, methacrylic acid, maleicanhydride, and N-substituted maleimides. Examples of non-rubber-modifiedstyrene polymers include polystyrene (PS) and acrylonitrile/styrenecopolymer (AS resin).

[0043] With respect to the styrene polymer used in the presentinvention, the reduced viscosity η_(sp)/C (as measured in a 0.005 g/cm³solution at 30° C.), which is a measure of the molecular weight, ispreferably in the range of from 30 to 80 cm³/g, more preferably from 40to 60 cm³/g, wherein, when the styrene polymer is a polystyrene resin,toluene is used as the solvent and when the styrene polymer is anunsaturated nitrile/aromatic vinyl copolymer, methyl ethyl ketone isused as the solvent. In the production of the styrene polymer, thereduced viscosity η_(sp)/C can be controlled by selecting the type andamount of the initiator, the polymerization temperature and the amountof chain transfer agent.

[0044] In the present invention, a resin mixture of aromaticpolycarbonate and styrene polymer is preferably used as resin component(a) when improvement in the melt fluidity of the aromatic polycarbonateis desired. The resin mixture used as resin component (a) preferably hasan aromatic polycarbonate content of 20% by weight or more, morepreferably from 50 to 95% by weight, that is, the styrene polymer of theresin mixture is 80% by weight or less, preferably from 5 to 50% byweight. When the aromatic polycarbonate content is less than 20% byweight, the heat resistance and mechanical strength of the ultimateshaped article become unsatisfactory. When the styrene polymer contentis less than 5% by weight, the improvement in the moldability of thearomatic polycarbonate resin composition becomes unsatisfactory.

[0045] The organopolysiloxane used as component (b) in the presentinvention is a component which plays an important role in impartingflame retardancy to the aromatic polycarbonate resin composition, andcomprises at least one linear organopolysiloxane (b)i and at least onecyclic organopolysiloxane (b)ii.

[0046] The above-mentioned linear organopolysiloxane (b)i is representedby the following formula:

[0047] wherein:

[0048] n represents an integer of 2 or more;

[0049] each R¹ independently represents a monovalent C₆-C₂₀ hydrocarbongroup containing an aromatic group;

[0050] each R² independently represents a monovalent C₁-C₂₀ hydrocarbongroup containing no aromatic group; and

[0051] each of R³ and R⁴ independently represents a hydrogen atom or atriorganosilyl group SiR⁵ ₃, wherein each R⁵ independently represents amonovalent C₁-C₂₀ hydrocarbon group.

[0052] The above-mentioned cyclic organopolysiloxane (b)ii isrepresented by the following formula:

[0053] wherein m represents an integer of 3 or more; and

[0054] R¹ and R² are as defined for formula (1) above.

[0055] In the present invention, R¹ in formulae (5) and (6) above whichrepresent a monovalent C₆-C₂₀ hydrocarbon group containing an aromaticgroup include alkyl groups substituted with aromatic hydrocarbongroup(s), aromatic hydrocarbon group(s) substituted with alkyl group(s),and also a monovalent C₆-C₂₀ aromatic hydrocarbon group, per se.Examples of hydrocarbon groups R¹ include a phenyl group, a tolyl group,a xylyl group, a benzyl group, a 2-phenylethyl group, a 1-phenylethylgroup, a 2-methyl-2-phenylethyl group, a naphthyl group and a biphenylgroup. Of these, a phenyl group is especially preferred.

[0056] Examples of hydrocarbon groups R² in formulae (5) and (6) aboveinclude alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl,pentyl, hexyl, and octyl groups; alkenyl groups such as a vinyl group;and cycloalkyl groups such as a cyclohexyl group. Of these, a methylgroup is especially preferred.

[0057] In the present invention, it is preferred that each R¹ informulae (5) and (6) above is a phenyl group and each R² in formulae (5)and (6) above is a methyl group. That is, the use of a linearphenylmethylsiloxane (homopolymer) as linear organopolysiloxane (b)i,and a cyclic phenylmethylsiloxane (homopolymer) as cyclicorganopolysiloxane (b)ii is especially preferred.

[0058] As apparent from formulae (5) and (6) above, each of linearorganopolysiloxane (b)i and cyclic organopolysiloxane (b)ii used in thepresent invention consists of D structures (R₂SiO_(1/2)). As describedabove, a branched organopolysiloxane mainly comprises branchedstructures such as T and Q structures, and is generally resinous. On theother hand, an organopolysiloxane consisting substantially of Dstructures is a linear or cyclic organopolysiloxane in an oil form, andsuch an organopolysiloxane has excellent fluidity as compared to that ofthe branched organopolysiloxane.

[0059] In addition, as compared to the branched organopolysiloxanemolecule, the organopolysiloxane molecule consisting substantially of Dstructures has a high content of hydrocarbon groups (i.e., R in theformulae above), relative to the content of silicon atoms. Therefore,the organopolysiloxane consisting substantially of D structures exhibitsan excellent dispersibility in aromatic polycarbonates and styrenepolymers as compared to that of branched organopolysiloxanes.

[0060] Moreover, for the reasons mentioned below, the organopolysiloxaneconsisting substantially of D structures is free from the problemsaccompanying the use of branched organopolysiloxanes, specifically theproblems caused by the presence of reactive terminal groups. Branchedorganopolysiloxanes containing high quantities of T and Q structures areproduced by a hydrolytic polymerization of multifunctional silanecompounds, such as trichlorosilane, tetrachlorosilane, trialkoxysilaneand tetraalkoxysilane, and contain a large amount, i.e. several percentto several tens of percent by weight of reactive terminal groups, suchas silanol groups or alkoxysilyl groups. Therefore, when the branchedorganopolysiloxane is incorporated into an aromatic polycarbonate at ahigh temperature, crosslinking of the organopolysiloxane per se as wellas lowering of the molecular weight of the aromatic polycarbonate arelikely to occur.

[0061] On the other hand, as described below, linear organopolysiloxane(b)i and cyclic organopolysiloxane (b)ii used in the present inventionare produced by a hydrolytic polymerization of bifunctional silanecompounds, such as dichlorosilane and dialkoxysilane. Molecules oflinear organopolysiloxanes (b)i may still contain the above-mentionedreactive terminal groups. However, in the case of linearorganopolysiloxanes, terminal groups are only present at the ends of themolecular chains i.e., two terminal groups per molecule, and thus theterminal group content per unit weight of a linear organopolysiloxane isextremely low. On the other hand, in the case of branchedorganopolysiloxanes, a large number of terminal groups is present in onemolecule (i.e., three or more terminal groups per molecule) and, thus,the terminal group content per unit weight of a branchedorganopolysiloxane is high. For this reason, the incorporation of linearorganopolysiloxane (b)i into an aromatic polycarbonate does not causethe above-mentioned problems occurring due to a large number of reactiveterminal groups.

[0062] When linear organopolysiloxane (b)i contains a silanol group at aterminal thereof, if desired, the chemical stability of linearorganopolysiloxane (b)i can be improved by blocking the terminal silanolgroups, namely by introducing a triorganosilyl group SiR⁵ ₃ wherein eachR¹ independently represents a monovalent C₁-C₂₀ hydrocarbon group, ontothe terminal silanol group of the linear organopolysiloxane molecule.With respect to the hydrocarbon group R⁵ of the triorganosilyl group, amethyl group or a phenyl group is especially preferred.

[0063] Cyclic organopolysiloxane (b)ii contains no reactive terminalgroups. Therefore, cyclic organopolysiloxanes (b)ii do not cause theabove-mentioned problems caused by reactive terminal groups.

[0064] In general, for enhancing the compatibility of anorganopolysiloxane with the aromatic polycarbonate and the styrenepolymer, it is required to increase an aromatic group content of anorganopolysiloxane molecule. By increasing the aromatic group content,the flame retardancy of the resultant resin composition can also beenhanced.

[0065] For increasing the aromatic group contents of linear and cyclicorganopolysiloxanes, it is necessary to use recurring units containingan increased amount of aromatic groups, namely the above-mentioned Dstructure in which the substituent R is a hydrocarbon group containingan aromatic group. As examples of such recurring units, there can bementioned recurring units respectively represented by the followingformulae (8) and (9):

[0066] wherein R¹ and R² are as defined for formula (5) above, and

[0067] wherein R¹ is defined in formulae (5) and (6) above.

[0068] The aromatic group content of the recurring unit represented byformula (9) (hereinafter, referred to as “recurring unit (9)”) is higherthan that of the recurring unit represented by formula (8) (hereinafter,referred to as “recurring unit (8)”). Therefore, the use of recurringunit (9) is advantageous for increasing the aromatic group content of anorganopolysiloxane.

[0069] However, the raw material for producing recurring unit (9) isexpensive. In addition, since recurring unit (9) contains two R¹ groupswhich are sterically bulky substituents, the polymerization of recurringunits (9) is difficult, so that it is difficult to produce, especiallyon a commercial scale, an organopolysiloxane comprising recurring units(9) only.

[0070] In addition, when an organopolysiloxane contains recurring units(9) in a large amount, the compatibility of the organopolysiloxane witha resin becomes too high. With respect to a shaped article obtained bymolding an aromatic polycarbonate resin composition containing such anorganopolysiloxane having too high a content of recurring units (9),when the shaped article burns, the plasticization and liquidization ofthe resin composition are likely to occur, leading to dripping offlaming particles. For this reason, an organopolysiloxane comprisingrecurring units (8) is preferably used in the present invention.

[0071] When an organopolysiloxane exhibits low compatibility with anaromatic polycarbonate and a styrene polymer, a problem is likely tooccur in that the organopolysiloxane is not uniformly and finelydispersed in the final shaped article, so that the article suffersnon-uniformity in coloring when colored, as well as the potential ofbleeding of the organopolysiloxane to the surface of the article.

[0072] The present invention is based on the novel finding that, whenlinear organopolysiloxane (b)i and cyclic organopolysiloxane (b)ii areused in combination, not only can the compatibility of theorganopolysiloxane with an aromatic polycarbonate and a styrene polymerbe improved, but also the dripping of flaming particles can beprevented, and as a result, a high level of flame retardancy is impartedto an aromatic polycarbonate.

[0073] In the present invention, it is required to use a linearorganopolysiloxane comprising recurring units (8) (i.e., linearorganopolysiloxane (b)i represented by formula (5) above) and a cyclicorganopolysiloxane comprising recurring units (8) (i.e., cyclicorganopolysiloxane (b)ii represented by formula (6) above).

[0074] The process for the production of the organopolysiloxanecomprising recurring units (8) can be conducted with ease, as comparedto the production of an organopolysiloxane comprising recurring units(9). Therefore, the organopolysiloxane containing recurring units (8) isalso advantageous from the viewpoint of a commercial production thereof.

[0075] The amount of cyclic organopolysiloxane (b)ii inorganopolysiloxane (b) is from 5 to 95% by weight, preferably from 10 to80% by weight, more preferably from 10 to 60% by weight, based on thetotal weight of linear organopolysiloxane (b)i and cyclicorganopolysiloxane (b)ii. When the amount of cyclic organopolysiloxane(b)ii is less than 5% by weight, the compatibility of organopolysiloxane(b) with the aromatic polycarbonate and the styrene polymer may becomeunsatisfactory. On the other hand, when the amount of cyclicorganopolysiloxane (b)ii is more than 95% by weight, the dripping offlaming particles is more likely to occur when the molded article burns.

[0076] There is no particular limitation with respect to the upper limitof the number of recurring units in cyclic organopolysiloxane (b)ii, but“m” in formula (6) is preferably 3 to 6. Cyclic organopolysiloxane (b)iiof formula (6) in which m is from 3 to 6 recurring units is especiallypreferred from the viewpoint of ease in production thereof and theeffect on improving the compatibility of organopolysiloxane (b) with thearomatic polycarbonate and the styrene polymer.

[0077] There is no particular limitation with respect to the molecularweight of linear organopolysiloxane (b)i, but the molecular weight of(b)i is preferably in a range such that the kinematic viscosity oforganopolysiloxane (b), comprising organopolysiloxanes (b)i and (b)ii),is in the range of from 10 to 1,000,000 mm²/sec, as measured at 25° C.in accordance with JIS-K2410. Such a kinematic viscosity is preferredfrom the viewpoint of volatility, kneadability and ease in handling withrespect to organopolysiloxane (b).

[0078] The amount of organopolysiloxane (b) used in the aromaticpolycarbonate resin composition is from 0.1 to 50 parts by weight,preferably from 0.5 to 20 parts by weight, relative to 100 parts byweight of a resin component (a). When the amount of organopolysiloxane(b) is less than 0.1 part by weight, the flame retardancy of thearomatic polycarbonate resin composition imparted by organopolysiloxane(b) is generally unsatisfactory. On the other hand, when the amount oforganopolysiloxane (b) is more than 50 parts by weight, the mechanicalproperties such as impact resistance of the aromatic polycarbonate resincomposition become disadvantageously low.

[0079] There is no particular limitation with respect to the method forproducing organopolysiloxane (b), and any conventional methods can beemployed. A conventional method for producing an organopolysiloxane is amethod in which an aromatic group-containing dichlorosilane R¹R²SiCl₂ oran aromatic group-containing dialkoxysilane R¹R²Si(OR)₂ (wherein Rrepresents an alkyl group) is subjected to hydrolytic polymerization. Bythis method there is generally obtained a mixture of linearorganopolysiloxanes (b)i having terminal silanol groups and cyclicorganopolysiloxanes (b)ii.

[0080] Linear organopolysiloxanes (b)i and cyclic organopolysiloxanes(b)ii can be separated from each other and purified. Linearorganopolysiloxane (b)i alone can be subjected to polymerization in thepresence of an acid catalyst or to equilibration polymerization, tothereby obtain linear organopolysiloxanes (b)i having a higher molecularweight.

[0081] The terminal silanol groups of linear organopolysiloxane (b)i maybe left as they are, but the terminal silanol groups can be blocked withR⁵ ₃Si group by using an appropriate reagent, such as R⁵ ₃SiCl or (R⁵₃Si)₂O (wherein each R⁵ independently represents a monovalent C₁-C₂₀hydrocarbon group) during the above-mentioned hydrolytic polymerization,equilibration polymerization or the like. By blocking the terminalgroups, the chemical stability of linear organopolysiloxane (b)i can beimproved.

[0082] The cyclic organopolysiloxane produced by the hydrolyticpolymerization can be used as cyclic organopolysiloxane (b)ii afterbeing separated and purified from the mixture of linear and cyclicorganopolysiloxanes. Alternatively, the obtained cyclicorganopolysiloxane (b)ii can be subjected to ring-openingpolymerization, to thereby convert cyclic organopolysiloxane (b)ii tolinear organopolysiloxane (b)i. The terminal groups of the resultantlinear organopolysiloxane (b)i can be controlled by using an appropriatetype of catalyst and optionally a terminator such as (R⁵ ₃Si)₂Omentioned above.

[0083] A mixture of linear organopolysiloxane (b)i and cyclicorganopolysiloxane (b)ii used as organopolysiloxane (b) can be obtainedby mixing a separately produced linear organopolysiloxane (b)i andcyclic organopolysiloxane (b)ii. Alternatively, the mixture of linearorganopolysiloxane (b)i and cyclic organopolysiloxane (b)ii produced bythe above-mentioned hydrolytic polymerization, as such, may be used.When linear organopolysiloxane (b)i and cyclic organopolysiloxane (b)iiare produced separately and mixed together, the recurring units oflinear organopolysiloxane (b)i and cyclic organopolysiloxane (b)ii maybe the same or different.

[0084] Each of linear organopolysiloxane (b)i and cyclicorganopolysiloxane (b)ii may be either a homopolymer or a copolymer.When an organopolysiloxane is a copolymer, the copolymer may be a randomcopolymer, a block copolymer or an alternating copolymer. Such anorganopolysiloxane copolymer can be obtained by using two or more typesof monomers having different R¹ and/or R², for example, two or moretypes of aromatic group-containing dichlorosilanes R¹R²SiCl₂ havingdifferent R¹ and/or R² and/or two or more types of aromaticgroup-containing dialkoxysilanes R¹R²Si(OR)₂ having different R¹ and/orR², wherein R represents an alkyl group.

[0085] The resin composition of the present invention may furthercomprise a flame retardant other than organopolysiloxane (b) to impart ahigh level of flame retardancy to the aromatic polycarbonate resincomposition. For example, use can optionally be made of at least oneflame retardant selected from the group consisting of (a) phosphatecompounds; (b) inorganic phosphorus compounds, such as red phosphorusand ammonium polyphosphate; (c) metal salts of organic sulfonic acids;(d) metal salts of organic sulfonamides or organic sulfonimides; (e)halogen-containing organic compounds; (f) nitrogen-containing organiccompounds, such as melamine, melamine cyanurate, melam, melem andmellon; and (g) inorganic metal compounds, such as magnesium hydroxide,calcium hydroxide, aluminum hydroxide, hydrotalcite, magnesiumcarbonate, calcium carbonate, zinc borate, antimony oxide, titaniumoxide, zirconium oxide and zinc oxide. Among these flame retardants,phosphate compounds (a), metal salts of organic sulfonic acids (c) andmetal salts of organic sulfonamides or organic sulfonimides (d) arepreferred in view of the low toxicity thereof and less lowering of thephysical properties of the final resin composition obtained by additionthereof.

[0086] Examples of phosphate compounds (a) include phosphates such astrimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributylphosphate, tripentyl phosphate, trihexyl phosphate, triphenyl phosphate,tritolyl phosphate, trixylyl phosphate, dimethyl ethyl phosphate, methyldibutyl phosphate, ethyl dipropyl phosphate, hydroxyphenyl diphenylphosphate; compounds obtained by introducing various substituents intothe above-mentioned phosphates; and condensed phosphate compoundsrepresented by the following formula (10):

[0087] wherein:

[0088] n represents an integer of 1 to 10;

[0089] each of Ar¹, Ar², Ar⁴ and Ar⁵ independently represents anaromatic group selected from the group consisting of a non-substitutedphenyl group and a phenyl group substituted with at least one C₁-C₁₀hydrocarbon; and

[0090] Ar³ represents a divalent C₆-C₂₀ aromatic hydrocarbon.

[0091] Examples of condensed phosphate compounds include bisphenol Atetraphenyldiphosphate, bisphenol A tetratolyldiphosphate, bisphenol Atetraxylylphosphate, bisphenol A di(phenylxylylphosphate) and resorcinoltetraphenyldiphosphate.

[0092] Examples of metal salts of organic sulfonic acids (c) includepotassium salts and sodium salts of organic sulfonic acids, such astrifluoromethanesulfonic acid, perfluoroethanesulfonic acid,perfluoropropanesulfonic acid, perfluorobutanesulfonic acid,perfluorohexanesulfonic acid, perfluorooctanesulfonic acid,trichlorobenzenesulfonic acid, diphenylsulfone-3-sulfonic acid,diphenylsulfone-3,3′-disulfonic acid and diphenylsulfone-3,4′-disulfonicacid. Of these, especially preferred are potassiumperfluorobutanesulfonate, potassium trichlorobenzenesulfonate andpotassium diphenylsulfone-3-sulfonate.

[0093] Examples of metal salts of organic sulfonamides or organicsulfonimides (d) include a potassium salt ofN-(p-tolyl-sulfonyl)-p-toluenesulfonimide and a potassium salt ofN-(N′-benzylaminocarbonyl)sulfanilimide.

[0094] Metal salts of organic sulfonic acids, or metal salts of organicsulfonamides or organic sulfonimides are used in an amount of from 0.001to 5 parts by weight, relative to 100 parts by weight of resin component(a). When the amount of such a metal salt is less than theabove-mentioned range, the effect of the metal salt to impart flameretardancy to the aromatic polycarbonate is low. When the amount of sucha metal salt is more than the above-mentioned range, the heat stabilityof the aromatic polycarbonate may decrease.

[0095] In the present invention, a fluoroolefin resin can be used toreduce the amount of flaming particles dripping from a molded articlewhen the article is on fire. As the fluoroolefin resins usable in thepresent invention, there can be mentioned homopolymers and copolymerscomprising fluoroethylene structures. Examples of fluoroolefin resinsinclude a difluoroethylene polymer, a trifluoroethylene polymer, atetrafluoroethylene polymer, a tetrafluoroethylene-hexafluoropropylenecopolymer, and a copolymer of tetrafluoroethylene and an ethylenemonomer containing no fluorine. Of these, polytetrafluoroethylene (PTFE)is preferred. There is no particular limitation with respect to themolecular weight and configuration of the fluoroolefin resin. However,when a fluoroolefin resin is incorporated into the resin composition, itis preferred that the fluoroolefin resin is dispersed in the resincomposition in the form of fibrils having a diameter of 0.5 μm or less.The amount of fluoroolefin resin incorporated into the resin compositionis in the range of from 0.1 to 0.5 parts by weight, relative to 100parts by weight of resin component (a). When the amount of fluoroolefinresin is less than the above-mentioned range, the effect of preventingthe dripping of flaming particles is low, while when the amount offluoroolefin resin is more than the above-mentioned range, both thefluidity and flame retardancy of the resin composition may suffer.

[0096] In the present invention, an auxiliary organic silicon compoundother than organopolysiloxane (b) can be additionally used to enhancethe flame retardancy of the resin composition of the present inventionas long as the organic silicon compound exhibits no adverse effect onthe properties of the resultant resin composition. Such an auxiliaryorganic silicon compound include polymers having a linear, branched,cyclic or three-dimensional network structure obtained by combining aplurality of at least one type of unit selected from the groupconsisting of M (R⁶ ₃SiO_(1/2)), D (R⁶ ₂SiO_(2/2)), T (R⁶SiO_(3/2)) andQ (SiO_(4/2)) structures. In general, R⁶ in the formulae above is ahydrogen atom; an alkyl group such as a methyl, ethyl, or propyl group;an alkenyl group such as a vinyl group; an aryl group such as a phenylgroup; or an alkoxy group such as a methoxy or ethoxy group. If desired,a functional group other than these groups, such as a hydroxyl group,can be used in combination with these groups. In this connection, itshould be noted that an organic silicon compound comprising theabove-mentioned recurring units (8) is excluded from the organic siliconcompounds usable herein. Among the organic silicon compounds, a siliconeresin comprising T structures, an MQ resin comprising M and Qstructures, and an MTQ resin comprising M, T and Q structures arepreferably used.

[0097] If desired, the flame retardant resin composition of the presentinvention may optionally contain various additives generally used withthermoplastic resins to improve moldability, impact resistance,stiffness, weatherability, appearance and the like. Examples ofadditives include heat stabilizers; antioxidants; ultraviolet lightabsorbers; weathering agents; antimicrobial agents; compatibilityagents; colorants (dyes and pigments); mold release agents; lubricants;antistatic agents; plasticizers; polymers, such as other resins andrubbers; and fillers. There is no particular limitation with respect tothe amount of additives used as long as the additives exhibit no adverseeffect on the properties of the flame retardant resin composition of thepresent invention.

[0098] With respect to the method for producing the flame retardantaromatic polycarbonate resin composition of the present invention, thereis no particular limitation, and conventional methods can be employed.For example, there can be mentioned:

[0099] a method in which a resin component (a) and an organopolysiloxane(b) are preliminarily mixed in a mixer, such as a Henschel mixer, asuper mixer, a tumble mixer and a ribbon blender, and the resultantmixture is melt-kneaded by means of an extruder, such as a single-screwextruder, a twin-screw extruder or a Banbury mixer;

[0100] a method in which a resin component (a) is melted in a staticmixer, a single-screw extruder, a twin-screw extruder or the like, andan organopolysiloxane (b) is added to and mixed with the melted resincomponent (a), whereupon the resultant mixture is melt-kneaded; and

[0101] a method in which a masterbatch is produced by melt-kneading apart of resin component (a), and a whole amount of organopolysiloxane(b) and optionally any other substances, such as a flame retardant otherthan organopolysiloxane (b), and then the masterbatch is added to theremainder of resin component (a), followed by melt-kneading. Thesemethods are illustrative and not limiting.

[0102] The flame retardant resin composition of the present inventioncan be advantageously used for producing housings and parts of officeautomation machines, data communication equipments, electric andelectronic appliances and household electric appliances, such ascopiers, facsimile machines, television sets, radios, tape recorders,video decks, personal computers, printers, telephones, data terminalequipment, portable telephones, refrigerators, microwave ovens, and thelike. The flame retardant resin composition of the present invention canalso be advantageously used for producing parts for automobiles.

[0103] The present invention will be further described in more detailwith reference to the following Examples and Comparative Examples, whichshould not be construed as limiting the scope of the present invention.

[0104] In the following Examples and Comparative Examples, the followingcomponents were used.

[0105] (A) Aromatic Polycarbonate PC: A commercially available bisphenolA type polycarbonate having a viscosity average molecular weight of20,000 (trade name: lupilon S3000, manufactured and sold by MitsubishiEngineering-Plastics Corporation, Japan);

[0106] (B) Styrene Polymer HIPS: A commercially available high impactpolystyrene (trade name: Styron, manufactured and sold by Asahi KaseiCorporation, Japan);

[0107] ABS: A commercially available ABS resin (trade name: Stylac ABS,manufactured and sold by Asahi Kasei Corporation, Japan);

[0108] (C) Organopolysiloxane:

[0109] (I): A linear phenylmethylsiloxane homopolymer, which wasproduced by hydrolytic polymerization of phenylmethyldichlorosilanewithout blocking the terminal silanol groups. This homopolymer containedapproximately 15% by weight of a cyclic tetramer (i.e.,tetramethyltetraphenylcyclotetrasiloxane), confirmed by gel permeationchromatography “GPC” and exhibited a kinematic viscosity at 25° C. ofapproximately 800 mm²/sec;

[0110] (II): A linear phenylmethylsiloxane homopolymer, which wasproduced by hydrolytic polymerization of phenylmethyldichlorosilanewithout blocking the terminal silanol groups. This homopolymer containeda cyclic tetramer (i.e., tetramethyltetraphenylcyclotetrasiloxane) and acyclic trimer (i.e., trimethyltriphenylcyclotrisiloxane), wherein thetotal content of the cyclic tetramer and cyclic trimer was about 26 byweight (confirmed by GPC), and exhibited a kinematic viscosity at 25° C.of approximately 600 mm²/sec;

[0111] (III): A commercially available linear phenylmethylsiloxanehomopolymer (trade name: PMM0021, manufactured and sold by Gelest, Inc.,U.S.A.), wherein the terminal groups of the homopolymer were blockedwith a trimethylsilyl group, confirmed by nuclear magnetic resonancespectroscopy “NMR”. This homopolymer contained approximately 3% byweight of a cyclic tetramer (i.e.,tetramethyltetraphenylcyclotetrasiloxane) (confirmed by GPC) andexhibited a kinematic viscosity at 25° C. of approximately 100 mm²/sec;

[0112] (IV): A commercially available linear phenylmethylsiloxanehomopolymer (trade name: PMM0025, manufactured and sold by Gelest, Inc.,U.S.A.), wherein the terminal groups of the homopolymer were blockedwith a trimethylsilyl group (confirmed by NMR). This homopolymercontained approximately 2% by weight of a cyclic tetramer (i.e.,tetramethyltetraphenylcyclotetrasiloxane) (confirmed by GPC) andexhibited a kinematic viscosity at 25° C. of approximately 500 mm²/sec;

[0113] (V): A commercially available cyclic tetramer ofphenylmethylsiloxane (i.e., tetramethyltetraphenylcyclotetrasiloxane)(trade name: LS8970, manufactured and sold by Shin-Etsu Chemical Co.,Ltd., Japan);

[0114] (VI): A commercially available linear copolymer ofdimethylsiloxane with diphenylsiloxane (phenyl group/methyl groupratio=25/75) (trade name: KF54, manufactured and sold by Shin-EtsuChemical Co., Ltd., Japan). This copolymer exhibited a kinematicviscosity at 25° C. of approximately 400 mm²/sec;

[0115] (VII): A commercially available linear copolymer ofdiphenylsiloxane and phenylmethylsiloxane (phenyl group/methyl groupratio=75/25) (trade name: PMP5053, manufactured and sold by Gelest,Inc., U.S.A.). This copolymer exhibited a kinematic viscosity at 25° C.of from 200,000 to 500,000 mm²/sec;

[0116] (VIII): An organopolysiloxane having a weight average molecularweight of about 20,000 measured by GPC using a calibration curveobtained with respect to standard polystyrene systems, phenylgroup/methyl group ratio=60/40, D structure/T structure ratio=20/80).This organopolysiloxane was produced by reacting phenyltrichlorosilane,methyltrichlorosilane and phenylmethyldichlorosilane with an excessamount of water, thereby conducting a hydrolytic condensation of thesesilane compounds.

[0117] (IX): A commercially available liquid phenylmethylpolysiloxanecomprising D structures and T structures (trade name: X-40-9235,manufactured and sold by Shin-Etsu Chemical Co., Ltd., Japan). Thisliquid phenylmethylpolysiloxane exhibited a kinematic viscosity at 25°C. of approximately 2,200 mm²/sec.

[0118] As flame retardants other than the above-mentionedorganopolysiloxanes, potassium perfluorobutanesulfonate (trade name:F114, manufactured and sold by DAINIPPON INK & CHEMICALS, INC., Japan)and polytetrafluoroethylene (trade name: Teflon 30J, manufactured andsold by Dupont-Mitsui Fluorochemical Co., Ltd., Japan), were used.

EXAMPLES 1 AND 6 TO 9, AND COMPARATIVE EXAMPLE 9

[0119] In accordance with the formulations indicated in Tables 1 and 2,the components were preliminarily mixed with each other. Using aKZW15-45MG type extruder (manufactured and sold by TechnovelCorporation, Japan), each of the resultant mixtures was individuallymelt-kneaded at 260° C., thereby obtaining a resin composition (in theform of pellet). Each of the obtained resin compositions wasindividually subjected to injection molding at a temperature of 260° C.by means of MJEC10 type injection molding machine (manufactured and soldby Modern Machinery Company, Japan), thereby obtaining test samples eachhaving a thickness of 3.18 mm.

[0120] The appearance of the test samples, especially with respect tothe bleeding of organopolysiloxane, was visually examined. Further,using the same test samples, the self-extinguishing properties of theresin compositions were evaluated in accordance with the VerticalBurning Method which is described in UL-94.

[0121] The results are shown in Tables 1 and 2.

EXAMPLES 2 TO 5 AND COMPARATIVE EXAMPLES 1 TO 8

[0122] In accordance with the formulations indicated in Tables 1 and 2,the components were preliminarily mixed with each other. Using aLaboplastomill (manufactured and sold by Toyo Seiki Co., Ltd., Japan),each of the resultant mixtures was individually melt-kneaded for 10minutes under conditions wherein the temperature was 220° C. and therevolution rate was 60 rpm, thereby obtaining a resin composition. Eachof the obtained resin compositions was individually subjected tocompression molding, thereby obtaining test samples each having athickness of 3.18 mm.

[0123] The appearance of the test samples, especially with respect tothe bleeding of organopolysiloxane, was visually examined. Further,using the same test samples, the self-extinguishing properties of theresin compositions were evaluated in accordance with the VerticalBurning Method which is described in UL-94. The results are also shownin Tables 1 and 2. TABLE 1 EX. 1 EX. 2 EX. 3 EX. 4 EX. 5 EX. 6 EX. 7 EX.8 EX. 9 COMPOSITION (a) PC 100 100 100 100 100 89 89 78 78 (Parts byHIPS — — — — — 11 — — — Weight) ABS — — — — — — 11 22 22 (b)i Linear (I)(II) (III) (IV) (IV) (II) (II) (II) (IV) Organo- 11.1 11.1 10.1 2.6 2.811.1 11.1 11.1 5.6 poly- siloxane (b)ii Cyclic (V) (V) (V) (IV) Organo-1.1 2.6 8.3 5.6 poly- siloxane Other F114 — — — — 0.1 0.5 0.5 0.5 0.5flame PTFE — — — — — — — 0.3 0.3 retardants Appear- ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ance EVALUATION Evaluation Average 3.5 4.1 4.5 6.6 3.9 4.8 4.6 4.7 4.2according flame-out to UL-94 time (sec) Dripping Not Not Not Not Not NotNot Not Not of flaming Ob- Ob- Ob- Ob- Ob- Ob- Ob- Ob- Ob- particlesserved served served served served served served served servedEvaluation V-0 V-0 V-0 V-1 V-0 V-0 V-0 V-0 V-0

[0124] TABLE 2 COMP. COMP. COMP. COMP. COMP. COMP. COMP. COMP. COMP. EX.1 EX. 2 EX. 3 EX. 4 EX. 5 EX. 6 EX. 7 EX. 8 EX. 9 COMPOSITION (a) PC 100100 100 100 100 100 100 100 100 (Parts by HIPS — — — — — — — — — Weight)ABS — — — — — — — — — (b)i Linear (III) (IV) — (VI) (VII) (VII) (VIII)(IX) — Organo- 11.1 11.1 11.1 11.1 5.3 11.1 11.1 poly- siloxane (b)iiCyclic — — (V) — — — — — — Organo- 5.3 poly- siloxane Other F114 — — — —— — — — — flame PTFE — — — — — — — — — retardants Appear- X X ◯ X ◯ ◯ XX◯ ◯ ance EVALUATION Evaluation Average 4.0 5.4 10.7 6.1 5.2 7.8 8.9 4.917.2 according flame-out to UL-94 time (sec) Dripping Not Not Not offlaming Ob- Ob- Ob- Ob- Ob- Ob- Ob- Ob- Ob- particles served servedserved served served served served served served Evaluation V-0 V-1 V-1V-1 V-1 V-1 V-1 V-1 Below the standards

[0125] The test sample produced in each of Examples 1 to 9 (in which alinear phenylmethylpolysiloxane was used in combination with a cyclictrimer or tetramer of phenylmethylpolysiloxane) had excellent appearanceand excellent self-extinguishing properties. Further, when each of thesetest samples was evaluated in accordance with UL-94, no occurrence ofdripping of flaming particles was observed.

[0126] On the other hand, although the test sample produced in each ofComparative Examples 1 and 2 in which a phenylmethylpolysiloxanecontaining almost no cyclic oligomer was used had excellentself-extinguishing properties, bleeding of the organopolysiloxane to thesurface of each of these test samples was observed and, thus, theappearance of each of these test samples was unsatisfactory.

[0127] The test sample produced in Comparative Example 3 in which only acyclic tetramer was used had excellent appearance. However, when thistest sample was evaluated in accordance with UL-94, dripping of flamingparticles was observed.

[0128] In Comparative Example 4 in which a linearphenylmethylpolysiloxane copolymer was used, wherein the content ofphenyl groups of the copolymer was low, the compatibility of thecopolymer with the aromatic polycarbonate resin was poor. As a result,with respect to the test sample produced in Comparative Example 4,bleeding of the organopolysiloxane to the surface of the test sample wasobserved.

[0129] In each of Comparative Example 5 and 6 in which a linearcopolymer of diphenylsiloxane with phenylmethylsiloxane was used, thecompatibility of the copolymer with the aromatic polycarbonate resin wasgood. However, when each of the test samples was evaluated in accordancewith UL-94, dripping of flaming particles was observed.

[0130] The test sample produced in each of Comparative Examples 7 and 8in which a silicone resin having a branched structure comprising Dstructures and T structures was used was tested in accordance withUL-94. In the test, dripping of flaming particles was observed. Withrespect to the test sample produced in Comparative Example 7, foamingwas observed on the surface of the test sample during the injectionmolding, and thus the test sample was brittle.

[0131] As apparent from the above, the resin composition of the presentinvention in which a linear phenylmethylpolysiloxane was used incombination with a cyclic trimer or tetramer of phenylmethylpolysiloxaneexhibits very excellent properties. As the resin composition of thepresent invention contains no halogen, exhibits excellent flameretardancy and moldability, and also exhibits excellent stability andappearance with respect to a molded article produced from the resincomposition, the resin composition of the present invention can besatisfactorily used as a material for parts of increasing size anddecreasing section such as parts for office automation machines, datacommunication equipment, electric and electronic appliances, householdelectric appliances, and automobiles.

What is claimed is:
 1. A flame retardant aromatic polycarbonate resincomposition comprising: 100 parts by weight of a resin component (a)comprising an aromatic polycarbonate and optionally a styrene polymer,wherein said resin component has an aromatic polycarbonate content of20% by weight or more relative to the weight of (a); and 0.1 to 50 partsby weight of an organopolysiloxane (b) comprising at least one linearorganopolysiloxane (b)i and at least one cyclic organopolysiloxane(b)ii, wherein said organopolysiloxane (b) contains component (b)ii inan amount of from 5 to 95% by weight, based on the total weight ofcomponents (b)i and (b)ii, said at least one linear organopolysiloxane(b)i having the following formula (1):

wherein: n represents an integer of 2 or more; each R¹ independentlyrepresents a monovalent C₆-C₂₀ hydrocarbon group containing an aromaticgroup; each R² independently represents a monovalent C₁-C₂₀ hydrocarbongroup containing no aromatic group; and each of R³ and R⁴ independentlyrepresents a hydrogen atom or a triorganosilyl group SiR⁵ ₃, whereineach R⁵ independently represents a monovalent C₁-C₂₀ hydrocarbon group;and said at least one cyclic organopolysiloxane (b)ii having the formula(2):

wherein m represents an integer of 3 or more; and R¹ and R² are asdefined for formula (1) above.
 2. The composition of claim 1, whereineach R¹ in said formulae (1) and (2) is a phenyl group and each R² insaid formulae (1) and (2) is a methyl group.
 3. The composition of claim1, wherein said cyclic organopolysiloxane (b)ii constitutes from 10 to80 percent by weight of organopolysiloxane (b) relative to the totalweight of (b)i and (b)ii.
 4. The composition of claim 1, wherein saidcyclic organopolysiloxane (b)ii constitutes from 10 to 60 percent byweight of organopolysiloxane (b) relative to the total weight of (b)iand (b)ii.
 5. The composition of claim 1, wherein m in said cyclicorganopolysiloxane is an integer from 3 to 6.